1. Field Of The Invention
The present invention relates generally to powered control and monitoring systems, such as industrial control networks. More particularly, the invention relates to a modular connector system including capacitors for enhancing performance of a power and data network.
2. Description Of The Related Art
A variety of control systems are known and are presently used in industry for communicating control and feedback signals between remote controllers, sensors and actuators. In a typical application, a process, such as a manufacturing or assembly line, will include a number of sensors for providing information relating to the manufacturing process, such as speeds of conveyors, speeds of motors, temperatures, pressures, feed rates, fluid levels, logical states of switches, and so forth. The sensed information is transmitted from the sensors to one or more control units which contain logic devices for processing the signals. A number of actuators will also typically be included for executing specific control functions or controlling various phases of the manufacturing process. The actuators might include motor controllers, electric relays, solenoid coils, and so forth. In most modem applications, the control circuit will include one or more microprocessors, solid state memory devices and other related circuitry appropriately programmed in accordance with the specific application. Based upon the sensed information and upon the program being executed by the controller, the controller will generate and transmit control or command signals to the actuators for carrying out the desired process. In many applications, a large number of sensed parameters and controlled actuators may be included to implement and control many facets of a manufacturing or other process.
In control and monitoring systems of the type described above, large scale networking is generally achieved by coupling the controllers, sensors and actuators to some type of shared network media. The network media permits the devices included in the network to communicate and receive data signals in accordance with predetermined protocols. To reduce the number of signal conductors required in the network media, the protocols typically permit devices to transmit and receive signals which are digitized or pulsed and encoded to include both address information and parameter information.
The type of network media employed in any particular application may vary depending upon the types of devices coupled to the network and their needs. In particular, certain monitoring and control networks provide only data signals without electrical power to the networked devices. In other applications, both data signals and electrical power are applied to the devices. In systems of the latter type, particular problems arise in providing a straightforward and reliable media package in which both power and data signals can be transmitted without adversely influencing the quality of data signal transmission due to the presence of power conductors and external fields generating differential mode noise, which can lead to errors in the transmission and recognition of data signals.
In one known approach, a pair of power conductors and a pair of signal conductors are twisted together in a media cable. The cable serves as a trunk line for transmitting both power and data signals between networked devices. The cable includes a shielding system around the conductors for reducing the adverse influences of both internal and external noise on the pulsed signals transmitted by the signal conductors. Network media of this type is commercially available from the Allen-Bradley Company of Milwaukee, Wisconsin under the commercial designation DeviceNet.
While networks and network media of the type described above provide excellent power and data transmission capabilities, they are not without certain drawbacks. For example, a shielded trunk cable is generally attached to device node connectors by removal of the cable shields and individually connecting power and data conductors to node connectors. This installation can be somewhat time-consuming. While other approaches have been proposed to reduce the time required for installation of power and data network systems, they pose other problems owing to their structure and function. For example, in one known system, power and data signals are transmitted in a two-conductor cable, the pulsed data signals being modulated on the power signals. The cable may be connected to node points by means of insulation displacement pins. However, special circuitry is generally required at each power supply and at each node point to properly modulate, demodulate and prevent corruption of the data signals.
There is a need, therefore, for an improved technique for transmitting power and data signals between networked devices which addresses the drawbacks of existing systems. In particular, there is a need for a network system in which a multi-conductor cable can be easily and quickly installed at node connectors in a relatively short time, while assuring reliable connection between a networked device and the power and signal conductors embedded in the cable. Moreover, there is a need for a network system of this type in which the adverse effects of both internal and external noise are reduced. Where a non-shielded cable is employed in the system for facilitating installation via insulation displacement pins, there is a need for a technique which will eliminate or reduce differential mode noise imposed on the signal conductors when a network device draws power from the power conductors.